Sealing off a firing chamber in a perforating tool



.5, J. HOOP Filed Jan. 23. 1969 SEALING OFF A FIRING CHAMBER INAPERFORATING r001,

C. POWER Sept 15, 1970 W ays I United States Patent 3,528,512 SEALINGOFF A FIRING CHAMBER IN A PERFORATING TOOL Billy Joe Boop, CorpusChristi, Tex., assignor to The Western Company of North America, Inc.,Fort Worth, Tex.

Filed Jan. 23, 1969, Ser. No. 793,391 Int. Cl. E21b 43/16 US. Cl.175-455 1 Claim ABSTRACT OF THE DISCLOSURE This specification disclosesmethod and apparatus for isolating a chamber in a perforating toolhaving a plurality of chambers and conductor means that connects anexplosive charge in one of the chambers to a firing means,

characterized by:

(a) providing a sealing partition means between the chamber with theexplosive charge and an adjacent chamber and having, connecting thechambers, a passageway through which the conductor means pass;

(b) providing a seat in the passageway;

(c) inserting a sealing projectile adjacent the seat and between theseat and the explosive charge; and

(d) detonating the explosive charge to drive the sealing projectile intothe seat.

This specification also discloses a specific construction of apparatusin which retaining means is provided behind the projectile and in whicha preferred projectile comprises:

(a) a cone-shaped guide portion no larger in diameter than the seat inthe partition means;

(b) a frustum portion larger in diameter than the seat to prevent theprojectile from passing completely through the seat; and V (c) aplurality of successively larger cylindrical portions connecting thecone-shaped guide portion with the frustum base portion.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to perforating tools. More particularly, it relates toperforating tools such as are employed in establishing communicationthrough casing between a well bore and subterranean formations.

Description of the prior art In producing hydrocarbon fluids fromsubterranean for mations, it is conventional practice, in completing awell in which casing has been set through the productive subterraneanformation, to perforate the casing to effect communication between thewell bore and the subterranean formation. Ordinarily, such communicationemploys the detonation of an explosive charge, either in jet perforatingor in driving a bullet through the casing, cement sheath thereabout, andinto the subterranean formation. The chambers housing the explosivecharges for efiecting perforations are conventionally relatively short;for example, on the order of a few feet or less. In many instances,therefore, it becomes necessary to employ a plurality of chambers toeffect perforations over the desired interval, which may extend for ahundred feet or more. In such an arrangement, the explosive charges inthe bottommost firing chamber will be detonated first, and theperforating proceed upward through successively higher firing chambers.It was early recognized that the later firing chambers must be isolatedfrom the earlier firing chambers to prevent damage and ensure thatsubsequent chambers will fire in their turn. The damage occurred notonly from the detonation itself, which often would prevent the firing orcause misfiring of the explosive charges in the subsequent chamber, butalso from the invasion of the bore hole fluids, ordinarily at arelatively high pressure. The pressure is usually greater at greaterdepth.

In the prior art, the respective chambers were isolated during assemblyof the tool, including the firing chambers. To seal against the hightemperatures and pressures with the conductors running through thesealing partition between the chambers created a diflicult sealingproblem, requiring expensive, elaborate and difiicultly assemblableseals. Thus, prior art processes of sealing each chamber during assemblyof the explosive charges, the explosive Primacord connecting thecharges, and the conductors passing to the respective chambers, toeffect an adequate seal; yet, ensure that the conductors would beoperative to fire the charges in the respective chambers; was a verycostly operation. Still further disadvantages attended the prior artseals since they were frequently unreliable and allowed some blow-by ofthe fluid during or after the detonation of the explosive charge in thechamber therebelow. This was particularly acute in wells deeper than9,000 feet, where the hydrostatic pressure on the fluids in the wellbore became significant; for example, about 4,000 lbs. per sq. in. withsalt water. Blow-by of hot detonation gasses was disadvantageous, aswould be expected, in that it could cause the explosive charges in thechamber immediately above to misfire or fire improperly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view partly in section andpartly schematic of a down hole perforating tool employing oneembodiment of the invention.

FIG. 2 is a longitudinal cross-section of a sealing partition employedin one embodiment of the invention.

FIG. 3 is a lateral cross-sectional view along the lines III-III of FIG.2.

FIGS. 4 and 5 are side views, partly in section, showing the sealingprojectile in place before and after detonation of an explosive chargein accord with one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) It is a particular feature ofthe invention to provide an isolation means effecting isolation of afiring chamber with a seal that resists extremely high pressures, thateliminates difliculties sealing around conducting means, and thatalleviates the other problems encountered in prior art devices; yet, toreduce labor costs to about 4: of that formerly required, to reducematerials costs for the seals to about of the former cost, and to reducemanufacturing costs for the partition means to about of that formerlyrequired.

In accordance with one aspect of the invention, there is provided animprovement in a method of isolating a chamber in a tool being used toperforate a steel casing thereabout, the tool having conductor meansleading into a plurality of chambers, the conductor means connecting anexplosive charge in one chamber to a firing means. The improvementcomprises:

(a) Providing a sealing partition means in the tool between the chamberhaving the explosive charge and an adjacent chamber, having a passagewayconnecting the chambers, and having the conductor means passing throughthe passageway;

(b) Providing a seat in the passageway;

(c) Inserting a sealing projectile adjacent the seat and between theseat and the explosive charge; and

(d) Detonating the explosive charge to drive the sealing projectile intothe seat and effect a seal to thereby isolate the chamber in which theexplosive charge has been fired from the adjacent chamber.

In accordance with another aspect of the invention there'is provided animprovement in a down hole tool for establishing communication through acasing from a Well bore into a subterranean formation by detonating anexplosive charge within one of a plurality of chambers in the tool. Theimprovement comprises:

(a) A partition means intermediate the one chamber containing theexplosive charge and an adjacent chamber and sealingly connected to thewalls thereof;

(b) A passageway passing through the partition means and communicatingwith both of the chambers;

(c) Conductor means within the passageway connecting the explosivecharge with a firing means;

(d) A seat provided in the passageway; and

(e) A sealing projectile adjacent the seat and between the seat and theexplosive charge.

The invention may be clearly understood by referring to the figure. FIG.1 illustrates apparatus for establishing communication through a casing11 from a wall bore filled with fluid 13 into subterranean formation 15.Therein tool 17 has a plurality of chambers 19 and 21. In chamber 19,perforating means, including explosive charges 23, are set to perforateinto the formation. In chamber 21 perforating means, including explosivecharges 25, are also set to perforate into the formation. Explosivecharges 23 are detonated by appropriate detonating means, such asPrimacord 27. Similarly, second detonating means, such as Primacord 29,serves to detonate explosive charges 25.

As a firing means, a DC power source 31 may be connected by conductors33 and 35 via a stepping switch 37 with Primacord 27 and explosivecharge 23. Conductor means, such as conductors 33 and 35, are carriedinside cable 39 which ordinarily has a tensile load bearing member inaddition to the conductors. Cable 39 may have an exterior armoredportion which will serve as a ground for the conductor means if desired.

Ordinarily, tool 17 is introduced into the well through a lubricator tomaintain the well pressure, especially after perforating. Cable 39,suspending tool 17, is lowered over a sheave and is lowered into andwithdrawn from the well in response to winching means. Additionally,depth measuring means may be employed in connection with cable 39 andits supporting sheave to position tool 17 in order to effectperforations at exactly the desired depth in the subterranean formation15. The lubricator, sheave, winching means and depth measuring means arewell known, and do not form any part of this invention and, hence, neednot be described herein.

Partition means 41 is interposed between chamber 19 and chamber 21.Partition means 41 is sealingly connected with wall 43 of chamber 19 andwith wall 45 of chamber 21. The connection may be effected by any means;such as, threaded bolts 47 having countersunk, recessed heads andpassing through the respective walls and into the partition means havingan aperture 49 tapped with matching threads, shown in greater detail inFIG. 2. The sealing may be effected by any means, such as O-rings 51mounted in grooves 53 and interposed between partition means 41 and thewalls 43 and 45 of the respective chambers 19 and 21.

Passageway 55 penetrates longitudinally through partition means 41. Theconductor means passing through passageway 55 connects explosive charges23 with the firing means. Seat 57 is formed in the passageway.Ordinarily, seat 57 is formed by reaming to a particular dimension for adepth; for example, about 1 inch; into passageway 55. If desirable, seat57 may be coated by a hard coating, such as silicon carbide or Stellite.

Sealing projectile 59 is positioned adjacent seat 57 such that it isbetween seat 57 and explosive charges 23 (FIG. 1)

It has been found advantageous to employ a retaining means such asenlarged portion 61 to maintain sealing projectile 59 adjacent seat 57and to help maintain it aligned therewith.

As can be seen in FIG. 3 threaded apertures 49 do not penetrate throughthe sidewall of the partition means to passageway 55;hence, there is noproblem of communication of fluids between the well bore and passageway55 except by way of chamber 19 following detonation of explosive charges23.

In operation, the components are assembled in tool 17 as describedhereinbefore. Thereafter, tool 17 is lowered, via cable 39 into wellbore 13 to the depth interval to be perforated. Stepping switch 37 isstepped onto conductor 33. This detonates Primacord 27, also detonatingexplosive charges 23 in chamber 19. The detonation of the explosivecharges 23 and Primacord 27 simultaneously perforates through casing 11into subterranean formation 15, and drives sealing projectile 59 deeplyinto seat 57 to isolate firing chamber 19. Thereafter, the gasesliberated by detonation of explosive charges 23 are dispelled throughopenings in chamber 19 into well bore 13.

Sealing projectile 59, in being driven into seat 57, severs conductor 33and seals against seat 57. In this way, misfiring of explosive charges25 in chamber 21 is prevented, either by damage from the detonationgases or from subsequent invasion of fluids from the pressurized wellbore 13 into chamber 21.

Stepping switch 37 can be stepped onto conductor 63, which, via itsconnection with DC power source through conductor 65, detonatesPrimacord 29; in turn, (1) detonating explosive charges 25, (2)isolating chamber 21 by driving its sealing projectile into its seat,and (3) perforating into the formation.

Thus, it can be seen that any number of chambers may be firedsuccessively to effect perforation over the desired interval byemploying this embodiment of the invention.

It has been found preferable to employ a back up material 65 (FIG. 2) inretaining means 61 and interposed between sealing projectile 59 andexplosive charges 23. Back up material 65' functions to help retainsealing projectile 59 in place adjacent seat 57 and aligned therewithbefore the detonation of charges 23; helps ensure that a maximumpressure is applied to the frustum base portion of sealing projectile 59to drive it deeply into seat 57; and disintegrates to fill any voidsthat might occur, block blow-by of any detonation gasses, and effectcomplete sealing. Back up material 65 is composed of short asbestosfiber formed into a disc. The asbestos fiber withstands high temperatureand yet disintegrates readily because of its short fiber to fulfill thedesired functions. Because it is asbestos, it may be pressed intoretaining means 61 without harming conductors that pass therethrough.

Sealing projectile 59 may be of any shape that will form a seal withseat 57. For example, sealing projectile 59 can be in the form of asphere or a cone. A cone having three sections differing in degree oftaper, or slope, from the adjacent section can be employed as thesealing projectile.

It has been found, however, that dramatically improved results areobtained when sealing projectile 59 has a shape illustrated in FIG. 4.Therein, cone-shaped nose portion 69 aids in assembly and alignment,automatically dispersing conductors such as conductor 33 around thesealing projectile. Cone-shaped nose portion 69 need not be completed toits apex but can be frusto-conical. Its maximum diameter will be nolarger than the diameter of seat 57. Preferably, cone-shaped noseportion has a slope with respect to its longitudinal axis of between 10and 30 degrees.

Next, there is a section 71 of at least two stepped cylindricalportions. First cylindrical portion 73, contiguous with the base of thecone-shaped nose portion 69, has a diameter substantially equal to theseat diameter. Thus, when sealing projectile 59 is driven into seat 57,first cylindrical portion 73 severs conductor 33, instead of merelycompressing it and allowing blow-by through openings at the edge of thecompressed conductor.

Second cylindrical portion 75 contiguous with first cylindrical portion73 has a diameter slightly larger than the seat diameter. The diameterof the second cylindrical portion is at least 0.002 inch, preferablyabout 0.005

7 inch, larger than the seat diameter. The second cylindrical portionserves to make the projectile self aligning in order to get sealmaterial all around the seat opening and somewhat cushion the impact ofthe projectile. The amount of metal larger than the seat must not be sogreat as to diminish the Wall to wall contact penetration into the seatto less than about A; inch. Although the maximum diameter will vary withthe materials of construction; ordinarily, the diameter of the secondcylindrical portion will be no more than about 0.010 inch larger thanthe seat diameter.

It has been found that improved results are obtained by including athird cylindrical portion 77 contiguous with the second cylindricalportion which has a diameter similarly slightly larger than the diameterof the second cylindrical portion. Specifically, similarly as describedwith respect to the second cylindrical portion and the seat diameter,the diameter of the third cylindrical portion is, ordinarily, 0.0020.0linch, preferably about 0.005 inch, larger than the second cylindricalportion. The third cylindrical portion 77 improves the self aligningcharacteristics of the projectile and by the additional metal around itsperiphery further cushions the impact of the projectile into seat 57;yet, does not accumulate metal so rapidly as to prevent the projectilefrom being driven deeply into the seat for a better seal.

Ultimately, there is a frustrum base portion 79, adjacent the lastcylindrical portion, that has a minimum diameter substantially the sameas the last cylindrical portion and sloping to a diameter at its baselarge enough to ensure that the projectile does not pass completelythrough the seat under the force of the explosive charge. Although themaximum diameter of the base will depend somewhat upon the material fromwhich sealing projectile 59 is made and on the degree of slope,ordinarily, a maximum diameter of at least 50% more than the diameter ofthe seat is adequate to ensure that the sealing projectile does not passcompletely through the seat. Preferably the frustum base portion has aslope of between 10 and 30 degrees with respect to its longitudinalaxis.

FIG. 5 illustrates sealing projectile 59 after it has been driven deeplyinto seat 57 by the detonation of explosive charges 23. Conductor 33 iscleanly severed. Excess metal 81 is driven onto the reamed seat and intoany small openings thereabout to effect a complete seal that isresistant to high temperature and high pressure.

Sealing projectile 59 may be constructed of any material that willresist the high temperature and high pressure; yet, be malleable enoughto be driven deeply into the seat to effect a seal. Ideally, thematerial of which the sealing projectile is constructed should belightweight such that it would have little inertia and will be movedinto sealing position quickly when the explosive charge is detonated. Itshould have a uniform density so as to truly align itself and properlyseat into seat 57. It should withstand temperature as high as 500degrees Fahrenheit down hole plus instantaneous temperature as high as1000 degrees Fahrenheit. It should be capable of shear and flow; i.e.,not be frangible; should have less hardness than the seat but shouldhave high enough density and resistance to shear and flow to keep frombeing forced completely through the seat. Specifically, soft, malleablemetals; such as, brass, copper, and mild steel may be employed. Aluminumis particularly preferred. Any other material having the desiredproperties can be employed.

A specific embodiment that has been found to work well in severaldifferent tools having different diameters was the following. Apassageway inch in diameter was drilled longitudinally through thepartition means. A retaining means inch in diameter was drilled 1 inchdeep into the passageway before the seat was formed. A seat inch wasreamed 1 inch deeper into the passageway. A sealing projectile wasfabricated of aluminum. It had a maximum diameter at the base of thefrustum base portion of about inch. T he'frustum base portion had aslope of about 13 degrees with respect to its longitudinal axis. Thecone-shaped nose portion had a slope of about 15 degrees with respect toits longitudinal axis and had a maximum diameter of 0.328 inch. Thefirst cylindrical portion had a diameter of 0.328 inch and a length of1.4 inch. The second cylindrical portion had a diameter of 0.333 inchand a length of inch. The third cylindrical portion had a diameter of0.338 inch and a length of inch. The overall length of the sealingprojectile was 1% inch, affording /2 inch each for the cone-shaped noseportion and the frustum base portion.

Thus, it can be seen that the invention provides a method of effecting aseal in situ, using the explosive force of the detonation of anexplosive charge, to effect a seal that is resistant to hightemperatures and to pressures in excess of 4,500 psi. The sealalleviates difiiculties with blow-by of fluid, either during thedetonation or from the well bore fluids following the detonation, thatcould cause misfiring of the explosive charges in the remainingchambers. Yet, even with the improved results, the invention effects acost reduction by cutting the labor costs on loading and assembling thegun in half, reducing the material cost for the seal itself to about theformer cost and reduces the manufacturing cost for the sub-assembly byabout 20%.

Although the invention has been described with a high degree ofparticularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the spirit and the scope of theinvention as hereinafter claimed.

What is claimed is:

. 1. In a method of isolating a chamber in a tool employed to perforatea casing thereabout, the tool having conductor means leading into aplurality of chambers, the conductor means connecting an explosivecharge in one chamber to a firing means, the improvement comprising:

(a) providing a sealing partition means in said tool between saidchambers, having a passageway connecting said chambers and having saidconductor means passing through said passageway;

(b) providing a seat in said passageway;

(c) inserting a sealing projectile adjacent said seat and between saidseat and said explosive charge; and

(d) detonating said explosive charge to drive said sealing projectileinto said seat.

References Cited UNITED STATES PATENTS 3,010,396 11/1961 Coleman 4.553,246,707 4/1966 Bell 175-4.55 X 3,327,792 6/1967 Boop 1754.55 X3,441,093 4/1969 Boop 175-455 DAVID H. BROWN, Primary Examiner s. 01.X.R. 16663

